This past weekend, I took my 1992 500E on a trip up a local "mountain" (Mount Diablo). Travel up to the 3800ft summit required travel along a long windy road. Ambient temperature was about 70 degrees (fahrenheit). After parking the car near the summit, I heard a gurgling sound coming from the engine compartment and noticed coolant leaking under the car. Lifting the hood, I could see that the coolant was "boiling" in the coolant resevoir, and being forced out through the overflow tube. I lost probably a half gallon of coolant as a result of the overflow.

When I started the car, the gurgling stopped. The temperature showing on the guage was what I would consider normal, given the trip up the mountain (between105 and 110). The gurgling started again when I cut the engine. When the gurgling completely stopped, the coolant resevoir was pretty much empty.

So what happened here? Was the car overheating but not registering on the temperature guage? Do I have an incorrect coolant/water mixture in the cooling system? Does the fact that fluids boil at lower temperatures at high altitudes (due to the lower pressure) explain the problem? Does Water Wetter have an adverse effect at high altitudes?

Any thoughts would be appreciated.

Thanks,

John

I am not sure if 3800 feet would be enough to cause the fluid to be visibly boiling. I have gone to 3600 feet on a spirited run out the Ortega highway several times, in 90 degree outside temperatures, and didn't loose any coolant when stopped at the top.

On the other hand, could your overflow tank have a bad cap or seal and be allowing the tank to depressurize?

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JCE
87 300E, 65k miles
Smoke Silver

This is not uncommon at altitude. Most caps are set to hold to about 14-15 psi at sea level. I can't give you the exact altitude/pressure correlation, but, the relative pressure inside the cooling system increases as altitude increases, even w/o overheating. Solution-> high pressure cap for life above the clouds. Or, your cap is not holding it's rated pressure and needs to be replaced.

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Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE



[This message has been edited by jeffsr (edited 09-05-2000).]

A poorly functioning coolant resevoir cap never occured to me! That would would certainly explain things. I will try a new cap and try the run again (this time, with some spare water in the trunk).

Thanks again,

John

also, I cannot imagine a a good 50-50 mix boiling at that altitude

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'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)

[QUOTE]Originally posted by revbond:
[B]A poorly functioning coolant resevoir cap never occured to me! That would would certainly explain things. I will try a new cap and try the run again (this time, with some spare water in the trunk).

Better make that spare *50/50* in the trunk, not pure H2O (which will definitely boil at 100C) .

Brian

After reading your post again, sounds like tome like you had pure water in your radiator and not the 50-50 mix that is recommended. I think at 5200 ft, the boiling point of water goes down a couple of degrees so the altitude thing has nothing to do with it. I think the gurgling stopped when the car was running because the water pump was running and as the water pump is running it is forcing liquid throughout the engine and pressurizing the system, increasing the boiling point, thus eliminating the gurgle in a nutshell. Once you cut off the engine, no more water pump, the de-pressurization of the 105-110 liquid (if not a 50-50 mix) will vaporize, thus causes the gurgle. That is probably why you were losing liquid out of the reservior. I would flush the system and replace with 50-50 mix and look for leaks.

I believe with a 50-50 mix, you would increase the boiling point of your cooling water from something like 212F to 250F, not sure. Also, removing vapors in your liquid will increase your heat transfer and your temp gauge will probably read around 95 to 100C instead of 105-110 C the next time you go up that mountain

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'89 420 SEL
'90 300 SEL
'68 Olds 88 Convertible
'84 300 SD (sold it)